text: William R. Newman traces the origins from the fourth book of Aristotle, Meteorology. The "dry" and "moist" exhalations of Aristotle became the alchemical sulfur and mercury of the eighth-century Islamic alchemist, Jābir ibn Hayyān (died c. 806–816). Pseudo-Gebers Summa perfectionis' contains an alchemical theory in which unified sulfur and mercury corpuscles, differing in purity, size, and relative proportions, form the basis of a much more complicated process.